Recent years have witnessed practical use of a flat-panel display in various products and fields. This has led to a demand for a flat-panel display that is larger in size, achieves higher image quality, and consumes less power.
Under such circumstances, great attention has been drawn to an organic EL display device that (i) includes an organic electroluminescence (hereinafter abbreviated to “EL”) element which uses EL of an organic material and that (ii) is an all-solid-state flat-panel display which is excellent in, for example, low-voltage driving, high-speed response, and self-emitting.
An active matrix organic EL display device includes, for example, (i) a substrate made up of members such as a glass substrate and TFTs (thin film transistors) provided to the glass substrate and (ii) thin film organic EL elements provided on the substrate and electrically connected to the TFTs.
A full-color organic EL display device typically includes organic EL elements of red (R), green (G), and blue (B) as sub-pixels aligned on a substrate. The full-color organic EL display device carries out an image display by, with use of TFTs, selectively causing the organic EL elements to each emit light at a desired luminance.
Thus, such an organic EL display device needs to be produced through at least a process that forms, for each organic EL element, a luminescent layer having predetermined pattern and made of an organic luminescent material which emits light of the above three colors.
Examples of known methods for forming such a luminescent layer having a predetermined pattern encompass a vacuum vapor deposition method, an inkjet method, and a laser transfer method. For example, the vapor deposition method is mainly used in a low-molecular organic EL display device (OLED) to pattern a luminescent layer.
The vacuum vapor deposition method uses a vapor deposition mask (also referred to as a shadow mask) provided with openings having a predetermined pattern. A thin film having a predetermined pattern is formed by vapor-depositing vapor deposition particles (vapor deposition materials, film formation materials) from a vapor deposition source on a vapor deposition target surface through the openings of the vapor deposition mask. In this case, the vapor deposition is carried out for each color of luminescent layers (This is referred to as “selective vapor deposition”).
The vacuum vapor deposition method is roughly classified into two methods: (i) a method for forming a film by fixing or sequentially moving a film formation target substrate′ and a vapor deposition mask so that the film formation target substrate and the vapor deposition mask are brought into close contact with each other; and (ii) a scanning vapor deposition method for forming a film while scanning a film formation target substrate and a vapor deposition mask which are provided so as to be spaced from each other.
The method (i) uses a vapor deposition mask similar in size to a film formation target substrate. However, use of the vapor deposition mask similar in size to the film formation target substrate makes the vapor deposition mask larger in size as the film formation target substrate is made larger in size. Thus, such an increase in size of the film formation target substrate accordingly easily causes a gap between the film formation target substrate and the vapor deposition mask by self-weight bending and extension of the vapor deposition mask. Therefore, according to a large-sized substrate, it is difficult to carry out patterning with high accuracy and positional displacement of vapor deposition and/or color mixture occur(s). This makes it difficult to form a high-definition vapor-deposition pattern.
Further, as the film formation target substrate increases in size, not only the vapor deposition mask but also a frame or the like that holds, for example, the vapor deposition mask is made enormously large in size and weight. Thus, the increase in size of the film formation target substrate makes it difficult to handle, for example, the vapor deposition mask and the frame. This may cause a problem with productivity and/or safety. Further, a vapor deposition device itself and the accompanying devices are also made larger in size and complicated. This makes device design difficult and increases installation cost.
Moreover, the large vapor deposition mask has problems concerning deflection, a weight, and a cost, and also a great problem that a mask production circumstance has not been ready in terms of, for example, processing a material of a vapor deposition mask, patterning, and bonding of a frame.
In view of the problems, great attention has recently been drawn to a scanning vapor deposition method for carrying out vapor deposition while carrying out scanning by use of a vapor deposition mask which is smaller than a film formation target substrate (see, for example, Patent Literatures 1 and 2).
According to such a scanning vapor deposition method, a band-shaped vapor deposition mask, for example, is used, and that vapor deposition mask is, for example, integrated with a vapor deposition source. Then, vapor deposition particles are deposited onto an entire surface of a film formation target substrate while at least one of (i) the film formation target substrate and (ii) the vapor deposition mask and the vapor deposition source is moved with respect to the other.
Thus, the scanning vapor deposition method, which makes it unnecessary to use the vapor deposition mask similar in size to the film formation target substrate, can reduce the size of the vapor deposition mask.